Conventionally, ink jet recorders which perform recording by ejecting ink onto a recording medium are widely used. In recent years, ink jet recorders have been used not only as home printers or office printers for preparing documents, postcards, and the like, but also used as the printers for performing recording for displays placed outdoors or the like. In this case, in order to prevent color fade-out and discoloration, solvent-based ink is used, and recording is performed on a sheet of chloroethylene, paper, or the like.
Specifically, the ink ejected from an ink jet recording head reaches the recording medium on a platen, whereby recording is performed. At this time, when time for drying ink droplets adhered to the recording medium is long, there is a problem in that the adjacent ink droplets are mixed with each other, thereby causing bleeding or a blurred image. Further, in a case where the ink drying time is long, in consideration to the drying time, a working efficiency becomes significantly low, for example, it is difficult to increase recording speed, and there is required a large space for storing the recording medium, which has undergone recording, until the ink is dried. In particular, in a case of using a relatively large recording medium such as a display placed outdoors, it is extremely troublesome to handle the recording medium after recording and before the ink is dried. Further, there is known that, in a case where the solvent-based ink is dried through air drying in a long period of time, color tone changes and a desired color does hot develop.
Patent Document 1 (JP-A-2000-108325) discloses a structure of an ink jet imaging system (plotter), which is provided with a heater in order to promote the drying of the ink. It is conceived that, also in the case where the solvent-based ink is used for recording, the structure disclosed in Patent Document 1 may be applied and heating is performed by the heater to quickly dry the ink.
As described above, in the case where the heater is used to heat the recording medium after the recording to thereby quickly dry the ink, it is thought to be the most effective that the heater is directly mounted to the platen for supporting the recording medium at a position facing the ink jet recording head. In particular, the platen formed of metal has high heat conductivity and easily transfer the heat of the heater to the recording medium. Therefore, if the heater is mounted to the metal platen, drying speed of the ink increases, which contributes to increase of the recording speed.
In the case of the large recording medium such as the display placed outdoors, the metal platen for supporting the recording medium is also large. In a case of a planar platen, with increase in size and weight thereof, it becomes difficult to firmly support the platen only by supporting at end portions thereof. It is desirable to support the planar platen using a substantially entire surface thereof, but it is not practical from the viewpoints of costs and a structure. Therefore, it is common to support the platen at a plurality of positions by using a plurality of support members aligned in a longitudinal direction of the platen.
In order to achieve recording with high accuracy, it is required for a gap between a nozzle of the ink jet recording head and the recording medium to be precisely and uniformly maintained at all times. To achieve this, positional accuracy and dimensional accuracy of the platen for supporting the recording medium so as to face the ink jet recording head are important. In general, the platen is formed of a metal such as aluminum or iron, and is finished by extruding or shaving with high dimensional accuracy (for example, with a tolerance of about 20 to 30 μm). As a matter of course, high dimensional accuracy is required also for the support members for supporting the platen. Hence, the support members are formed of a metal such as aluminum or iron as well as the platen, and are finished by shaving with high dimensional accuracy. As described above, in the structure in which the plurality of metal support members are used to support the metal platen, high dimensional accuracy is obtained.
However, since the metal such as aluminum or iron has high heat conductivity, a part of the heat transferred from the heater to the platen escapes to a frame or the like through the support members. As described above, the platen is, supported at the plurality of positions by the support members aligned in the longitudinal direction of the platen. Therefore, in the thus constructed platen, an amount of the escape of heat transferred from the heater is small in positions away from the support members, thereby being capable of promoting the drying of the ink. Besides, an amount of the escape of heat transferred from the heater is large in the vicinity of the support members, thereby causing drying of the ink to be relatively slow. Due to the escape of the heat through the support members as described above, there is caused partial temperature difference in the platen. Due to the partial temperature difference caused in the platen, there generate a part where the ink is dried fast and a part where the ink is dried slowly on the recording medium. This results indifferences in dot diameter (size) or shape owing to, for example, differences in how the ink spreads, or constitutes a factor for color shading or reduction in recording accuracy.
It is therefore an object of the present invention to provide an ink jet recorder in which the escape of the heat transferred from the heater to the platen may be reduced and the partial temperature difference caused in the platen is suppressed, thereby being capable of performing favorable recording.